This invention relates to an adjustable-in-length insert for raising the grade of a generally rectangular grating that resides in a catch basin frame or in a similar manhole frame or utility access hole. It usually is installed preparatory to repaving or resurfacing the pavement around the top of the frame. The term "catch basin frame" will be used for simplicity herein to mean any utility access hole frame fitted with a removable grating.
Unique problems are involved in such installation. In the typical frame the grating rests on and is supported mainly by the end sills of the frame, and, if the frame also has a roadway-side (as distinguished from the curb side or pavement edge side) longitudinal sill, then by such longitudinal sill also. Ordinarily there is little if any support for the grating along the curb side of the frame, and often the only support for it is at each end of the frame. Thus, when the grating is removed and the adjustable raising insert is fitted tightly in the frame, there is at least one and sometimes there are two long gaps under the sides of the insert where the insert lacks support.
To extend or foreshorten the sides of the inserts conventionally from their middles or ends (e.g. with slip-joints or screw-operated extender joints) puts undesirable strain on such end or side joints and incurs attendant risk.
Such inserts and their joints often must stand up to heavy axle loads and impact loads from vehicles and snow plows without a hazardous failure. Even if the rest of the side of an insert is heavy and strong, the length-adjusting joints of the insert can be very vulnerable to malfunction or, worse, to failure.
Another problem is the fitting of the insert to a catch basin frame that has a curb box, and many of them do. This adds vertical impedance features which must be accommodated.
Additionally, as there are often only the collar elements rising from the two end sills of the frame to react against most if not all of the insert-tightening pressure, it is especially desirable to exert a great deal of force against these elements. This is to get thereby as much frictional grip on the insert as possible; this supplements the mechanical hooks, clamps and like hold-down means that attach the insert to the in-place catch basin structure or manhole structure below.
The instant insert overcomes the lack of curb side support, and it need not be unusually heavy to do so; it also can be made to accommodate a curb box handily; and it is capable of being fitted very tightly between and against the collar elements on the end sills of the catch basin frame.